1. Field of the Invention
This invention relates to the classification of paper from a variety of contaminated paper-plastic mixtures from miscellaneous sources. More specifically for example, this invention relates to the recovery of high grade paper fibers from municipal solid waste (hereinafter MSW) which includes municipal household garbage and trash and includes such trash as is normally collected by a municipality, as for example, household garbage and trash, household yard trash, commercial trash from retail establishments, apartments, offices and warehouses. In addition, this invention relates to a classification method to recover valuable materials from selected wastes such as vegetable fibers, paperboards, agricultural and industrial cellulose materials as well as old corrugated boxes from supermarkets, wadding and molded pulps.
This invention finds particular utility for classicfication of valuable fibers from the "light weight fraction" of MSW herein after LW-MSW which is composed of mainly papers, textiles, and plastics. The light weight fraction of the MSW is defined as trash MSW which has been first prepared to remove heavy materials such as stones, iron or other metal objects, glass, carpeting, construction debris, wire, rubber, tires, and white goods.
Such materials are removed by solid waste crushing and shredding followed by use of rotary or flat screens, magnets, or otherwise. The present invention enables the recovery of the paper fibers from contaminated paper-plastic mixtures such that the paper cellulose fibers are refined and suitable for direct repulping by paper mills into commercial grade papers, including paper products, molded fibers, building materials, and the like. In addition this product is a suitable fuel. This process also produces other classified products which are suitable fuels and have other uses.
2. Description of the Prior Art
Various attempts have been made to find uses for the light weight fraction of MSW. Air classifiers of various types have been employed which have attempted to recover useable cellulose fibers. Such process provides a cellulose product having limited use since it is contaminated in significant amounts with plastics and other contaminants which can be used only for low grade products such as soil conditioners or fuel.
Other prior art processes have attempted to directly repulp in water the MSW or plastic-paper mixture recovered from MSW. Such process have proved ineffective because of the extreme difficulty in separating the plastics and contaminants from the paper fraction. An example of such a prior art process, which recovered low grade plastic contaminated paper confetti from a paper-plastic mixture, is found in my application Ser. No. 427,301 filed Jan. 7, 1974. Therein combined air classifications were used following steady cooking of the mix followed by drying by forced hot air to attempt reaching a cleaned paper fiber product.